Premature Thrust Reverser Activation During Final Approach (ZP-CDP)

Incident Overview and Sequence of Events The aircraft was on a scheduled international flight carrying eighteen passengers. During the final approach to runway 10, the pilot reported that at approximately 20 meters above the runway threshold, the propellers on both engines reversed. The pilot stated that the mechanic reported the occurrence at the same moment. The aircraft began nosing down and tilting to the left. The pilot applied right rudder and attempted to nose up, but the aircraft did not respond despite the application of power. The aircraft struck the runway surface, and both engines and the left wing were torn off. The aircraft went out of control, veered off the runway, and came to rest upside down in a grassy area approximately 250 meters from the runway end. All 24 occupants were injured, and the aircraft was destroyed. The crew consisted of pilot René Ferreira, copilot Pablo Romero, flight engineer Zacarías Soto, radio operator Marcial Quiñónez, purser Néstor Arrúa, and stewardess Elodia González. ## Official Findings and Probable Cause The official investigation concluded that the accident was due to the premature operation of the reversing system while the aircraft was on final approach at a height of 20 meters. This caused the aircraft to stall and lose lift, leading it to drop to the ground, slew round, and turn over. The investigation noted that the electro-mechanical reverse safety device installed on the landing gear was inoperative. This device is designed to close an electric circuit and free the throttle lock only when the left landing gear strut is compressed, requiring the aircraft to touch down and roll for some distance before the throttles can be moved to reverse the propellers. The inoperative safety mechanism allowed the levers to be moved back and the propeller reversing system to operate before the landing gear had made contact with the runway. The investigation considered the inoperative reverse lock safety system a deficiency in maintenance, even if it had been intentionally adjusted by the crew or during overhauls. The pilot-in-command was found to have acted incorrectly and imprudently by prematurely operating the propeller reversing system during the final approach instead of following the required procedure of applying reverse propellers during the landing run. The statements by the crew members were disregarded in favor of the evidence indicating premature operation of the reversing system. ## Unofficial Report An unofficial report stated that a paper cup was placed on the center console by the crew. On final approach, the content of this cup poured on the gear levers, causing an electrical short-circuit that caused the activation of the thrust reversers.